The present invention relates generally to cooktops, and more particularly, to a radiant electric heater unit for cooktops and radiant electric heater units having a temperature sensor that measures differences in reflected radiant energy.
Radiant electric heating units, as is well-known in the art, comprise an electrical heating element such as a coil heating element, or a ribbon heating element. In conventional heating units, the ends of the heating element connect through a thermal switch or limiter to an electrical circuit by which current is supplied to the heating element. The unit is installed beneath a cooking surface upon which utensils are placed. When a utensil is placed on the top of the cooking surface, the utensil is heated by direct radiant energy passing through the cooking surface. The utensil is also partially heated by conduction through absorbed radiant energy in the cooking surface. The thermal switch is responsive to the heating unit temperature exceeding a preset temperature to open the circuit path between a power source and the heating element to cut off current flow to the heating element. When the temperature falls back below the preset temperature, the switch reconnects the circuit path to restore the current flow to the heating element.
There are a number of problems with these heating units. One of these is the thermal switch. The thermal switch is expensive, representing 20-30% of the total cost of a heating unit. The switch assembly is a primary source of heating unit failure. It is simply too expensive to replace a failed switch. Rather, when the switch fails, the heating unit is discarded and a new heating unit is substituted in its place. Elimination of the existing thermal switch would not only be a substantial cost savings, but would also improve the service life of a heating unit; provided, that proper temperature control of the heating unit is still maintained. Moreover, these heating units are installed beneath a sheet of glass-ceramic material. This makes removal and installation difficult if the heating unit fails.
There is also a need for boiling liquids faster. Typical heating units drive the temperature to a particular set point without regard to the type of utensil that is on the heating unit or its location. The type of utensil and its location on the heating unit can affect system performance and the time to boil liquids. For example, a concave utensil reflects radiant energy back into the heating unit. A xe2x80x9chot spotxe2x80x9d may be formed in the glass-ceramic material underneath the concave portion of the utensil. The pocket of air under the concave portion of the utensil will serve as an insulator, preventing the spot from cooling. Moreover, an off-center utensil can cause portions of the glass-ceramic material not covered by the utensil to reach excessive temperatures. Without knowing the type of utensil or its location on the heating unit, these extreme conditions must be considered when determining the maximum temperature set point in the heating unit. This may result in a lower maximum set point for all types of utensils. A lower maximum set point, however, increases the time to boil liquids in flat pans that are centered correctly. Thus, a further need exists for a heater unit design that allows a controller to determine the type of utensil and whether it was centered properly.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
To that end, the present invention includes a support for a temperature sensor in a heating unit. The temperature sensor has a sensing element and lead wires. The heating unit has a heating element that radiates direct radiant energy. The support includes an insulating post having an upper head portion and a lower base portion. The upper head portion has a recess to house at least a portion of the sensing element of the temperature sensor. The recess shields at least a portion of the sensing element of the temperature sensor from the direct radiant energy of the heating element. The base portion has at least one hole to receive the lead wires of the temperature sensor.
The head portion of the insulating post may have slots to receive the lead wires of the temperature sensor. The support may further have at least one insulating cover to shield the lead wires from the direct radiant energy of the heating element. The insulating post may be made of ceramic or other insulating materials. In one embodiment, the support is made of ceramic material such as L-3 Steatite. The temperature sensor may be a Platinum Resistance Temperature Detector (platinum RTD).
In another embodiment, the present invention is a temperature sensor assembly for a heating unit. The heating unit has a heating element that radiates direct radiant energy. The temperature sensor assembly includes a temperature sensor and a support post. The temperature sensor has a sensing element and lead wires. The support post has an upper head portion and a lower base portion. The upper head portion has a recess to house at least a portion of the sensing element of the temperature sensor. The recess shields at least a portion of the temperature sensor from the direct radiant energy of the heating element. The base portion has a means for receiving the lead wires of the temperature sensor.
In a further embodiment, the present invention is a heating unit adapted to be installed in a cooktop. The operation of the heating unit is controlled by a controller. The heating unit includes a cooking plate, a support pan, an insulation layer, a heating element, a temperature sensor, and a support post. The support pan is disposed beneath the cooking plate. The insulation layer is supported in the pan and includes an insulation base and an insulation sidewall ring. The heating element is supported on the insulation base in a spaced apart relationship to the cooking plate. The heating element is capable of radiating direct radiant energy. The temperature sensor senses the temperature inside the heating unit and includes a sensing element and lead wires. The support post has an upper head portion and a lower base portion. The upper head portion has a recess to house at least a portion of the sensing element of the temperature sensor. The recess also shields at least a portion of the sensing element from direct radiant energy of the heating element.
The heating unit may be self-contained and modular with respect to the cooktop. The cooking plate is made of as infrared transmissive material such as glass-ceramic. The insulation base has a hole to receive at least a portion of the support post. The hole and the portion of the support post inserted into the hole are shaped to prevent movement of the support post in relation to the insulation base. An insulating paste or cement may further be used to retain the support post in the hole of the insulation base. The temperature sensor may be a platinum RTD.
The above summary of the present invention is not intended to represent each embodiment, or every aspect of the present invention. This is the purpose of the figures and detailed description that follows.